FERMENTATION WITH SPECIAL REFERENCE TO THE SUGAR HOUSE. 



immersion alcoholometer. Thus spirit showing 40-0 over proof by the alcohol- 

 ometer, and of actual strength 43 '1 over proof is said to have an obscuration 

 of 3'1 ; in some cases, however, the obscuration is expressed on the proof 



O.-l 



spirit, so that for the example quoted the obscuration is y7^j-:==2-17percent. 

 on proof spirit. 



The easiest method of determining the obscuration is as under : 



1. Take the apparent strength by the hydrometer. 



2. Evaporate about 200 c.c. of the spirit on a water bath till all the 

 alcohol is removed; take up the residue with water, and make up to the volume 

 of the spirit taken. 



3. Take the density of the solution of the residue either by the pycno- 

 meter or by a hydrometer graduated to read -0001. It is absolutely essential 

 that all measurements be made at the temperature at which the instruments 

 are graduated. 



Calculation : Let x =. specific gravity of the obscured spirit, and d = 



/* 



specific gravity of the residue dissolved in water; then == original gravity of 

 the spirit. 



Example: Coloured rum stands 21 Sikes at 84 F., indicating an 

 apparent strength of 40'6 O.P. ; the specific gravity corresponding to 21 Sikes 

 is -8512. The density of the residue dissolved in water is 1-0040. Then 



,o t -I O 



original gravity of spirit = , Q Q = -8478. The Sikes indication corresponding 



to a specific gravity of -8478 is 19*0, indicating a spirit 42'8 O.P. ; hence the 

 obscuration is 42-8 40'6 2*2. 



An older formula for use with this method gives x d = original gravity 

 of the spirit. 



A second method, and cne generally used for beers and wines, consists of 

 distill r ng over the material until all the alcohol has passed over, rraking the 

 distillate up to the original volume and finding the strength of the distillate by 

 an immersion alcoholometer, which in the absence of solids in solution gives 

 exact results; with strong spirit, such as rum, it is extremely difficult, 

 if not impossible, to prevent loss by evaporation and the first method is 

 preferable. 



In the following table are calculated obscurations from the observed 

 density of the residue dissolved in water, the standards adopted for the calcula- 



537 



